1. Field
The present invention relates to an ultrasound color Doppler image system, and more specifically, to an ultrasound color Doppler image system that filters a clutter signal from a color Doppler image.
2. Description of the Related Art
An ultrasound color Doppler image system may emit an ultrasound to a human body and may measure a Doppler shift frequency of the ultrasound reflected from a blood flow, thereby detecting a distribution of the blood flow in a real time.
Although the emitted ultrasound is well focused on the blood flow, a part of the ultrasound may be emitted in an undesired direction, and thus, a reflection signal reflected from the blood flow may be returned together with an undesired signal reflected from other tissue besides the blood flow. In this instance, the reflection signal from the blood flow is referred to as a Doppler signal, and the undesired signal reflected from other tissue is referred to as a clutter signal.
Usually, when the ultrasound is well focused, most of ultrasound energy may be transmitted to a focal point, and a relatively small portion of the ultrasound energy may leak to the outside, and thus, a desired signal from the focal point may be mostly returned. However a reflectivity of blood flow is relatively small compared with a reflectivity of peripheral tissue, such as a vessel wall, a muscle, and the like, and thus, in general, the clutter signal is greater than the Doppler signal even though a relatively small amount of ultrasound energy generally leaks.
When there is little movement of the peripheral tissue, a Doppler shift frequency is relatively close to zero, and thus, it is generally well-known that the clutter signal is easily eliminated by a high-pass clutter filter. Also, when movement of the peripheral tissue becomes faster, the Doppler shift frequency of the clutter signal may increase. Accordingly, the clutter signal may not be completely eliminated with a general clutter filter, and thus, an aberrant color may appear on a screen. The fast movement of the tissue may be displayed as though the fast movement is the blood flow. The aberrant color is an artifact displayed on the screen, and the artifact may appear as an instantaneous flash on the screen, thereby being referred to as a flash artifact.